Fats (Lipids)

Fats are a concentrated form of energy. Per unit of weight, they contain 2¼ times as much energy as either carbohydrates or proteins. (Fats provide approximately 9 kcal per gram.) They also supply a source of essential fatty acids to aid in metabolic processes. Normally 1 to 2% fat will supply the necessary amount of essential fatty acids. The remainder of the dietary fat is used as an energy source. Since fat is a concentrated source of energy, it is used as a convenient ingredient to increase the dietary energy. Fat tends to make feeds and some food more palatable to animals and people. Other nutrients must be properly adjusted in high-fat diets to ensure that the animal still gets the proper balance of essential nutrients as they are satisfied on less feed.

The product fact sheet includes levels of fatty acids in the diets: linoleic, linolenic, arachidonic, Omega-3, total saturated, and total monounsaturated. Considerable research attention has been given to omega-3 fatty acids in recent years. In grain-based diets, omega-3 fatty acids are derived primarily from the use of fish meal and soy oil in the products. Antioxidants are used to help prevent rancidity. As fat is oxidized, the rancidity increases the destruction of fat-soluble vitamins, creates unpleasant odors, and decreases palatability. Antioxidants are not added directly to most grain-based diets, but they are added at low levels by suppliers of some ingredients, such as fish meal, meat meal, or animal fat to prevent oxidative rancidity.

Fats in Purified Diets

Most purified diets are made with a base amount of soy oil or corn oil as a constant source of essential fatty acids (EFA). Typically when additional fat above the minimally-required level is required, porcine lard is used as the source. Occasionally other sources of fat will be used in addition to or in place of lard, such as soy oil, corn oil, coconut oil, and hydrogenated vegetable fat (“Crisco”).

For a contemporary approach, see the TestDiet^® 21st Century Western Diet Series™ comprised of diets using multiple sources of fats, including multiple sources of EFA.

We also formulate diets with reduced or no EFA, see EFA-Deficient Diets.

Which fats are most suitable for custom diets?

Humans and mammals in general need fats in their bodies and in their diets. Animals use fat for energy storage because stored fat provides nine KCal/g of energy, while carbohydrates and proteins provide only four KCal/g of energy. Fat also cushions vital organs, like the kidneys, and serves as insulation, especially just beneath the skin.

Fatty acids that contain no carbon-carbon double bonds are termed saturated fatty acids, while fats that contain at least one double bond in the fatty acid are termed unsaturated fats. Saturated fatty acids of less than eight carbon atoms are liquid at physiological temperature, whereas those containing more than ten carbon atoms are solid at room temperature.

“High-fat” diets (generally considered those in excess of 30-40 kcal% fat) are commonly used in research to study atherosclerosis, obesity, diabetes, hyperlipidemia, and other diseases/conditions.

There are many fat sources to consider when designing a diet for a specific research study. Below, several of the fat sources are provided along with some pertinent nutrient information that may help with the design of a diet and help meet the objectives of an experiment.

	Fatty Acids, %*
FAT SOURCE	Saturated Fat	Mono- unsaturated Fat	Poly- unsaturated Fat	Linoleic Acid (18:2)	Linolenic Acid (18:3)	Cholesterol, mg
Plant Sources
Coconut Oil	86.1	6.2	1.9	2.1	0.0	0.0
Corn Oil	13.3	24.2	58.0	57.2	0.9	0.0
Cottonseed Oil	25.8	19.0	51.3	51.8	0.3	0.0
Crisco Vegetable Shortening	25.0	33.0	25.0	-	-	0.0
Olive Oil	14.3	70.9	10.4	9.3	0.7	0.0
Palm Oil	47.2	40.2	9.9	10.6	0.2	0.0
Peanut Oil	18.1	45.8	29.9	30.6	0.0	0.0
Safflower Oil–High Linoleic	8.5	13.0	75.1	76.2	1.0	0.0
Safflower Oil–High Oleic	9.1	78.5	14.0	14.5	0.5	0.0
Sesame Oil	14.2	38.5	42.8	41.3	0.5	0.0
Soy Oil	14.5	22.5	57.8	51.0	7.3	0.0
Sunflower Oil–High Linoleic (>60.0%)	11.1	18.6	69.0	70.0	0.7	0.0
Sunflower Oil–High Oleic	9.7	83.6	3.8	3.6	0.3	0.0

Animal Sources
Beef Tallow	49.8	41.8	4.0	3.1	0.6	109.0
Butter	50.9	22.2	3.0	2.7	0.3	215.0
Cod liver Oil	20.8	46.4	28.8	1.2	0.8	570.0
Lard	40.5	43.6	10.7	9.9	0.7	95.0
Margarine, 80% Fat	15.3	36.5	24.2	20.9	2.2	0.0
Menhaden Fish Oil	27.1	20.4	29.9	1.2	1.4	521.0
Pork Animal Fat	39.7	44.2	12.1	11.0	0.6	143.0

* Values are an estimated average of published values (McCance and Widdowson. 1993. The Composition of Foods (5^th Edition). The Royal Society of Chemistry.; NutritionData. 2006. www.nutritiondata.com ) and Land O'Lakes Purina Feed’s formulation system.